I just checked out the Zend.com site. They have a version of Zend Optimizer (2.0.3) for Mac OS X that works with PHP 4.1, but they haven't yet released a version (2.1) that works with PHP 4.3. Zend Optimizer 2.1 is already available for Linux, Windows, and Solaris, so I have no idea why the Mac OS X version is lagging along.
Unfortunately, since the Zend Optimizer is closed source software, I can't produce an updated version fo Mac OS X and I'm 99.94% positive none of the other versions will work on a Mac.
I'm sorry to say, but I think the best way to find out when this is coming is to contact Zend directly. (http://www.zend.com/store/contact.php) Hopefully they can provide an answer.